In recent years, neurodegenerative disease has become an important concern due to the expanding elderly population which is at greatest risk for these disorders. Neurodegenerative diseases include the diseases which have been linked to the degeneration of neural cells in particular locations of the central nervous system (CNS), leading to the inability of these cells to carry out their intended function. These diseases include Alzheimer's Disease, Huntington's Disease, Amyotrophic Lateral Sclerosis, and Parkinson's Disease. In addition, probably the largest area of CNS dysfunction (with respect to the number of affected people) is not characterized by a loss of neural cells but rather by abnormal functioning of existing neural cells. This may be due to inappropriate firing of neurons, or the abnormal synthesis, release, and processing of neurotransmitters. These dysfunctions may be the result of well studied and characterized disorders such as depression and epilepsy, or less understood disorders such as neurosis and psychosis. Moreover, brain injuries often result in the loss of neural cells, the inappropriate functioning of the affected brain region, and subsequent behavior abnormalities.
Consequently, it is desirable to supply neural cells to the brain to compensate for degenerate or lost neurons in order to treat neurodegenerative diseases or conditions. One approach to this end is to transplant neural cells into the brain of the patient. This approach requires a source of large amounts of neural cells, preferably from the same individual or a closely related individual such that host-versus-graft or graft-versus-host rejections can be minimized. As it is not practical to remove a large amount of neurons or glial cells from one person to transplant to another, a method to culture large quantity of neural cells is necessary for the success of this approach.
Another approach is to induce the production of neural cells in situ to compensate for the lost or degenerate cells. This approach requires extensive knowledge about whether it is possible to produce neural cells in brains, particularly adult brains, and how.
The development of techniques for the isolation and in vitro culture of multipotent neural stem cells (for example, see U.S. Pat. Nos. 5,750,376; 5,980,885; 5,851,832) significantly increased the outlook for both approaches. It was discovered that fetal brains can be used to isolate and culture multipotent neural stem cells in vitro. Moreover, in contrast to the long time belief that adult brain cells are not capable of replicating or regenerating brain cells, it was found that neural stem cells may also be isolated from brains of adult mammals. These stem cells, either from fetal or adult brains, are capable of self-replicating. The progeny cells can again proliferate or differentiate into any cell in the neural cell lineage, including neurons, astrocytes and oligodendrocytes. Therefore, these findings not only provide a source of neural cells which can be used in transplantations, but also demonstrate the presence of multipotent neural stem cells in adult brain and the possibility of producing neurons or glial cells from these stem cells in situ.
It is therefore desirable to develop methods of efficiently producing neural stem cells for two purposes: to obtain more stem cells and hence neural cells which can be used in transplantation therapies, and to identify methods which can be used to produce more stem cells in situ.